A Levels or GCE Advanced Level is an intensive course study which prepares students for learning at higher levels. It requires a high level of study skills and motivation. It is one of the main academic routes into higher education. The wide range of subjects offered allows the student to take courses to suit his own individual need. A Levels are studied as separate subjects over two years and are assessed mostly by examination. Most universities in UK require students applying for undergraduate programmes to do the A Levels, however they also welcome students with other international qualifications.

So if you are planning to go to UK for your undergraduate studies and are very sure of it, you can opt for the A Levels instead of doing Std XII. You do not need to take the O Levels and as for the A Levels, you should have completed your Std X.